Leroy R. Grumman Cadet Squadron, NER-NY-153

Civil Air Patrol - The official auxiliary of the United States Air Force

Rocket Engines/Motors


A rocket engine does not use rotational energy to run.  They are reaction engines.  The principle of it is that the fuel contained within the body of the rocket is rapidly/explosively expanded and expelled out of the tail cone nozzle of the rocket.  This reaction then causes thrust and propels the rocket forward.  This is an example of one of Sir Isaac Newton's fundamental laws, "For every action, there is an equal and opposite reaction".


The type of mechanism used to produce exhaust material distinguishes rocket engines. The simplest "engine" is a compressed air bottle attached to a nozzle. The exhaust gas is stored in the same form as it appears in the exhaust. Ejection of compressed air, or other gas, from a nozzle is a perfectly satisfactory rocket operation for some purposes.


          Rocket thrust is the reaction force produced by expelling particles at high velocity from a nozzle opening. These expelled particles may be solid, liquid, or gaseous. The engine's ability to produce thrust will endure only so long as the supply of particles, or working fluid, holds out. Expulsion of material is the essence of the thrust production, and without material to expel no thrust can be produced, regardless of how much energy is available.



Solid Fuel Rockets

Solid fuel rockets are the first rockets to be recorded in history.  They were first invented in ancient China, and have been used ever since. The chemical make up of a solid rocket fuel is very similar to the chemical makeup of gunpowder. However, gunpowder explodes, making it unusable, so the chemical composition has been altered to make it burn fast, but not explode. In the solid-chemical rocket, the fuel and oxidizer are intimately mixed together and cast into a solid mass called a grain. To make a rocket work, a fast burning nonexclusive fuel is needed.  One of the biggest problems with solid fuel rocket engines is that once started, the reaction cannot be stopped or restarted.  This makes them considered uncontrollable.  Therefore, solid fuel rockets are more widely used for missiles, or as booster rockets.








Solid Fuel Model Rocket Engine




Liquid Fuel Rockets


The first liquid fuel rocket was produced by Robert Goddard in 1926. The idea of liquid fueled rocket is easy to grasp.  A fuel and an oxidizer (in Goddard’s case, he used gasoline and liquid oxygen) are pumped into a combustion chamber.  A reaction takes place, and it expands propelling the rocket forward.  The expanding gas is then forced through a nozzle that makes them accelerate to a higher velocity.


The fuel and oxidizer may be fed to the combustion chamber by pumps or by pressure in the tanks (see diagram below). Propellant flow rates must be extremely large for high-thrust engines, often hundreds of gallons per second. Pump-fed systems may require engines delivering several thousand horsepower to drive the pumps. This power is usually developed by a hot gas turbine, supplied from a gas generator that is actually a small combustion chamber. The main rocket propellants can also be used for the operation of the gas generator in a non-pressurized system.



Liquid Fuel Rocket Engines - Pump-fed vs Pressurized


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